During the production of gas and/or oil by a hydrocarbon well, the multiphase fluid mixture stream that flows through the perforations of the casing made facing a hydrocarbon bearing zone is often laden with solid particles. Such solid particles include sand grains, silts, clays and other subterranean formation materials. The solid particles are dragged from the formation layers by the fluid flow and carried by the fluid flow into the well towards the surface. These solid particles may damage the production equipments, either by their erosive actions, or by settling down in parts of the production equipment, thus causing well plugging, pipes erosion, and severe contamination of the production equipments. These may require regular cleaning of the production equipment during which hydrocarbon production is stopped. All these detrimental effects of the solid particles onto the production are costly. Thus, there is a need to monitor the fluid flow and to identify the zones responsible of solid particles entries into the well in order to allow operators to take the necessary steps when excessive amounts of solid particles are found to be present in the fluid flow. Implementing corrective actions may include the installation of sand screens or even closing the responsible zones with patches.
Various methods of investigating a hydrocarbon well to determine solid particles, in particular sand entry from a subterranean hydrocarbon-bearing formation into the well are known in the art.
The documents U.S. Pat. Nos. 3,509,764, 3,563,311, and 4,315,428 describe standalone well tools performing acoustic measurements.
The document U.S. Pat. No. 3,509,764 describes a method of investigating a cased well including a tubing string extending through a producing zone. The method consists in positioning a sound detector inside the tubing string adjacent the zone and monitoring the sound created by the impingement of the well production stream from the producing zone on the exterior of the tubing string. The possible clogging of perforations, resulting in excessive flow velocity of the well stream through unclogged perforations and consequent abrasion of the tubing string, can be detected. The method is only sensitive to indirect impacts on the tubing.
The document U.S. Pat. No. 3,563,311 describes a method of investigating a well penetrating a fluid-bearing formation with a sound detector. The well is produced at a plurality of flow rates under conditions such that fluid flowing from the formation impinges against an interface within the well. The sound produced by the impingement of this fluid is monitored by the sound detector at each flow rate. From the information thus obtained, the flow rate and location at which sand is produced from the formation may be determined. The detector is only sensitive to indirect impacts on the tubing.
The document U.S. Pat. No. 4,315,428 describes a sensor for detecting sand grains in a fluid flow. The sensor comprises a ring-shaped member carrying an acoustic transducer. The ring-shaped member is supported on a rod by clamping means, and material having elastic properties is arranged on the surfaces of the ring-shaped member that contact the rod or the clamping means. The sensor is disposed in the well and only exposed to transversal impacts.
The documents US 2007/047867 and U.S. Pat. No. 4,240,287 describe other techniques relying on sensors positioned outside or across the pipe in which the fluid flows.
The document US 2007/047867 describes a downhole fiber optic acoustic sand detector. An array of fiber optic acoustic sensors (Bragg gratings) is formed within an optical fiber. The array of acoustic sensors may be deployed to a well bore for detecting acoustic signals occurring within the production area of the well bore, such as acoustic signals resulting from sand invading the well bore. A plurality of acoustic sensors may be formed by forming a plurality of periodic refractive index perturbations at selected intervals within the acoustic sensing section of the optical fiber. The fiber optic acoustic sensor may be deployed in the well or may be unobtrusively mounted on the exterior of a well casing.
The document U.S. Pat. No. 4,240,287 describes a method and apparatus for detecting sand particles in a flowing fluid, e.g. the production from a gas or oil well. An acoustic transducer is used to detect the sand particles and the resulting signal is filtered to pass a frequency band of 50 to 500 kilohertz. A pulse height discriminating means and pulse counter is provided for counting the number of pulses that exceed a pre-set amplitude.
The drawbacks of such conventional solutions are that an accurate quantitative evaluation of sand production/entry requires complex data treatment and relies on transducer sensitivity calibration that may not be accurate, and/or may drift, and/or may be dependent on temperature variation.